This SMART CUT® technique employs the following steps:
a) bombarding a first face of a substrate, for example, formed from silicon, with hydrogen or rare gas type light ions, for example, helium, to implant the ions in a sufficient concentration into the substrate and create a layer of weakening micro-cavities;
b) bringing the face of the substrate into intimate contact with a stiffener or receiving substrate; and
c) fracturing/splitting at the layer of micro-cavities by applying a heat treatment and/or mechanical detachment stress, such as inserting a blade at the level of the layer of micro-cavities, applying tensile, bending and/or shear stresses, and/or applying ultrasound or microwaves of suitable power and frequency.
By detaching a portion of the implanted substrate, the SMART CUT® method can produce a thin film with a homogeneous thickness substantially corresponding to the distance between the face of the bombarded substrate and the layer of micro-cavities formed by implantation.
Compared with other known methods of fabricating thin films, such as the method known as “SIMOX” (described in the document “SIMOX SOI for Integrated Circuit Fabrication,” Hon Wai Lam, IEEE Circuits and Devices Magazine, July 1987) or methods of thinning a wafer by chemical or any other chemical-mechanical abrasion, that do not require very high implantation doses, nor an etch-stop barrier.
However, with “SIMOX”, the bulk of the transferred thin film contains a simple metal (Al), transition metals (Ti, Cr, Fe, Co, Ni, Cu, Zn, etc), alkali metals (Li, Na, K etc), alkaline-earth metals (Mg, Ca, Ba, etc), halogen (F, Br, Cl), metalloid (As), or organic types of contaminants (C, N, O) as contaminating impurities. Those impurities correspond to impurities present in the starting substrate and/or impurities introduced by the method employed. As an example, the presence of transition metal type impurities may cause large variations in the electrical properties in the transferred thin film.